1、Designation: D 6011 96 (Reapproved 2003)Standard Test Method forDetermining the Performance of a Sonic Anemometer/Thermometer1This standard is issued under the fixed designation D 6011; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the dy-namic performance of a sonic anemometer/thermomete
3、r whichemploys the inverse time measurement technique for velocityor speed of sound, or both. Performance criteria include: (a)acceptance angle, (b) acoustic pathlength, (c) system delay, (d)system delay mismatch, (e) thermal stability range, (f) shadowcorrection, (g) velocity calibration range, and
4、 (h) velocityresolution.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prio
5、r to use.2. Referenced Documents2.1 ASTM Standards:2C 384 Test Method for Impedance and Absorption ofAcoustical Materials by the Impedance Tube MethodD 1356 Terminology Relating to Sampling and Analysis ofAtmospheresD 5527 Practice for Measuring Surface Wind and Tempera-ture by Acoustic MeansE 380 P
6、ractice for Use of the International System of Units(SI) (the Modernized Metric System)3. Terminology3.1 DefinitionsFor definitions of terms related to this testmethod, refer to Terminology D 1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 axial attenuation coeffcienta ratio of the fre
7、e streamwind velocity (as defined in a wind tunnel) to velocity along anacoustic propagation path (vt/vd) (1).33.2.2 critical Reynolds number (Rc)the Reynolds numberat which an abrupt decrease in an objects drag coefficientoccurs (2).3.2.2.1 DiscussionThe transducer shadow corrections areno longer v
8、alid above the critical Reynolds number due to adiscontinuity in the axial attenuation coefficient.3.2.3 Reynolds number (Re)the ratio of inertial to viscousforces on an object immersed in a flowing fluid based on theobjects characteristic dimension, the fluid velocity, and vis-cosity.3.2.4 shadow c
9、orrection (vdm/vd)the ratio of the truealong-axis velocity vdm, as measured in a wind tunnel or byanother accepted method, to the instrument along-axis windmeasurement vd.3.2.4.1 DiscussionThis correction compensates for flowshadowing effects of transducers and their supporting struc-tures. The corr
10、ection can take the form of an equation (3) or alookup table (4).3.2.5 speed of sound (c, (m/s)the propagation rate of anadiabatic compression wavec 5 gP/r!s0.5(1)where:P = pressurer = density,g = specific heat ratio, ands = isentropic (adiabatic) process (6).3.2.5.1 DiscussionThe velocity of the co
11、mpression wavedefined along each axis of a Cartesian coordinate system is thesum of propagation speed c plus the motion of the gas alongthat axis. In a perfect gas (5):c 5 gR* T/M!0.5(2)The approximation for propagation in air is:cair5 403 T 1 1 0.32 e/P!#0.55 403 Ts!0.5(3)1This test method is under
12、 the jurisdiction of ASTM Committee D22 onSampling and Analysis of Atmospheres and is the direct responsibility of Subcom-mittee D22.11 on Meteorology.Current edition approved April 10, 2003. Published June 2003. Originallyapproved in 1996. Last previous edition approved in 1996 as D 6011 - 96.2For
13、referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the list of referenc
14、es at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.6 system clockthe clock used for timing acousticwavefront travel between a transducer pair.3.2.7 system delay (dt, s)the time delay through thetransduc
15、er and electronic circuitry (7).3.2.7.1 DiscussionEach path through every sonic arrayaxis can have unique delay characteristics. Delay (on the orderof 10 to 20 s) can vary as a function of temperature anddirection of signal travel through the transducers and electroniccircuitry. The average system d
16、elay for each axis in an acousticarray is the average of the delays measured in each directionalong the axisdt 5 dt11dt2!/2 (4)3.2.8 system delay mismatch (dtt, s)the absolute differ-ence in microseconds between total transit times ttin eachdirection (tt1, tt2) through the system electronics and tra
17、nsduc-ers.3.2.8.1 DiscussionDue principally to slight differences intransducer performance, the total transit time obtained with thesignal originating at one transducer can differ from the totaltransit time obtained with the signal originating at its pairedtransducer. The manufacturer should specify
18、 the system delaymismatch tolerance.dtt5 ? tt12 tt2? (5)3.2.9 thermal stability range (C)a range of temperaturesover which the corrected velocity output in a zero windchamber remains at or below instrument resolution.3.2.9.1 DiscussionThermal stability range defines a rangeof temperatures over which
19、 there is no step change in systemdelay.3.2.10 time resolution (Dt, s)resolution of the internalclock used to measure time.3.2.11 transit time (t, s)the time required for an acousticwavefront to travel from the transducer of origin to thereceiving transducer.3.2.11.1 DiscussionTransit time (also kno
20、wn as time offlight) is determined by acoustic pathlength d, the speed ofsound c, the velocity component along the acoustic propaga-tion path vd, and cross-path velocity components) vn(8)t 5 dc22 vn2!0.56 Vd# /c22 vd21 vn2!# (6)The transit time difference between acoustic wavefront propagationin one
21、 direction (t1, computed for + vd) and the other (t2, computedfor vd) for each transducer pair determines the magnitude of avelocity component. The inverse transit time solution for the along-axisvelocity is (9)vd5d2F1t121t2G(7)The total transit times tt1and tt2, include the sum of actual transittim
22、es plus system delay through the electronics and transducers in eachdirection along an acoustic path, dt1and dt2. System delay must beremoved to calculate vd, that is,t15 tt12dt1(8)t25 tt22dt2(9)3.2.11.2 DiscussionProcedures in this test method includea test to determine whether separate determinati
23、ons of d t1anddt2are needed, or whether an average dt can be used. Therelationship of transit time to speed of sound isc25Fd2S1t111t2DG21 vn2(10)and the inverse transit time solution for sonic temperature in air is asfollows (6):Ts5 Sd21612DF1t111t2G21vn2403(11)3.2.12 velocity calibration range (Uct
24、o Us, (m/s)therange of velocity between creeping flow and the flow at whicha critical Reynolds number is reached.3.2.12.1 DiscussionThe shadow correction is valid over arange of velocities where no discontinuities are observed in theaxial attenuation coefficient.3.2.13 velocity resolution (dv, (m/s)
25、the largest change inan along-axis wind component that would cause no change inthe pulse arrival time count.3.2.13.1 DiscussionVelocity resolution defines the small-est resolvable wind velocity increment as determined fromsystem clock rate. For some systems, dv defined as the standarddeviation of sy
26、stem dither can also be reported.3.3 Symbols:c = speed of sound, m/s,Cp= specific heat at constant pressure, J/(kgK),Cv= specific heat at constant volume, J/(kgK),e = vapor pressure, Pa,d = acoustic pathlength, m,f = compressibility factor, dimensionless,M = molecular weight of a gas, g/mol,P = pres
27、sure, Pa,R* = universal gas constant, 8.31436 J/(molK),RH = relative humidity, %,t = transit time, s,tt= total transit time, s,T = absolute temperature, K,Ts= sonic absolute temperature, K,Uc= upper limit for creeping flow, m/s,Us= critical Reynolds number velocity, m/s,vd= velocity component along
28、acoustic propagationpath, m/s,vdm= tunnel velocity component parallel to the array axis(vt, cos u), m/s,vn= velocity component normal to an acoustic propaga-tion path, m/s,vt= free stream wind velocity component (unaffected bythe presence of an obstacle such as the acousticarray), m/s,dt = system de
29、lay, s,dtt= system delay mismatch, s,Dt = clock pulse resolution, s,a = acceptance angle, degree,g = specific heat ratio (Cp/Cv), dimensionless,dv = velocity resolution, m/s,u = array angle of attack, degree, andr = gas density, kg/m3.D 6011 96 (2003)23.4 Abbreviations:UnitsUnits of measurement are
30、in ac-cordance with Practice E 380.4. Summary of Test Method4.1 Acoustic pathlength, system delay, and system delaymismatch are determined using the dual gas or zero windchamber method. The acoustic pathlength and system clockrate are used to calculate the velocity resolution. Thermalsensitivity ran
31、ge is defined using a zero wind chamber. Theaxial attenuation coefficient, velocity calibration range, andtransducer shadow effects are defined in a wind tunnel. Windtunnel results are used to compute shadow corrections and todefine acceptance angles.5. Significance and Use5.1 This test method provi
32、des a standard method for evalu-ating the performance of sonic anemometer/thermometers thatuse inverse time solutions to measure wind velocity compo-nents and the speed of sound. It provides an unambiguousdetermination of instrument performance criteria. The testmethod is applicable to manufacturers
33、 for the purpose ofdescribing the performance of their products, to instrumenta-tion test facilities for the purpose of verifying instrumentperformance, and to users for specifying performance require-ments. The acoustic pathlength procedure is also applicable forcalibration purposes prior to data c
34、ollection. Procedures foroperating a sonic anemometer/thermometer are described inPractice D 5527.5.2 The sonic anemometer/thermometer array is assumed tohave a sufficiently high structural rigidity and a sufficiently lowcoefficient of thermal expansion to maintain an internal align-ment to within t
35、he manufacturers specifications over itsdesigned operating range. Consult with the manufacturer for aninternal alignment verification procedure and verify the align-ment before proceeding with this test method.5.3 This test method is designed to characterize the perfor-mance of an array model or pro
36、be design. Transducer shadowdata obtained from a single array is applicable for all instru-ments having the same array model or probe design. Somenon-orthogonal arrays may not require specification of trans-ducer shadow corrections or the velocity calibration range.6. Apparatus6.1 Zero Wind Chamber,
37、 sized to fit the array and accom-modate a temperature probe (Fig. 1) used to calibrate the sonicanemometer/thermometer. Line the chamber with acousticfoam with a sound absorption coefficient of 0.8 or better (TestMethod C 384) to minimize internal air motions caused bythermal gradients and to minim
38、ize acoustic reflections. Installa small fan within the chamber to establish thermal equilibriumbefore a zero wind calibration is made.6.2 Pathlength ChamberSee Fig. 2.6.2.1 Design the pathlength chamber to fit and seal an axisof the array for acoustic pathlength determination. Constructthe chamber
39、components using non-expanding, non-outgassingmaterials. Employ O-ring seals made of non-outgassing mate-rials to prevent pressure loss and contamination. Design thechamber for quick and thorough purging. The basic pathlengthchamber components are illustrated in Fig. 2.6.2.2 Gas Source and Plumbing,
40、 to connect the pathlengthchamber to one of two pressurized gas sources (nitrogen orargon). Employ a purge pump to draw off used gases. Requiredpurity of the gas is 99.999 %.6.3 Temperature Transducer (two required), with minimumtemperature measurement precision and accuracy of 60.1Cand 60.2C, respe
41、ctively, and with recording readout. One isrequired for the zero wind chamber and one for the pathlengthchamber.6.4 Wind Tunnel:6.4.1 Size, large enough to fit the entire instrument arraywithin the test section at all required orientation angles. Designthe tunnel so that the maximum projected area o
42、f the sonicarray is less than 5 % of tunnel cross-sectional area.FIG. 1 Sonic Anemometer Array in a Zero Wind ChamberFIG. 2 Pathlength Chamber for Acoustic PathlengthDeterminationD 6011 96 (2003)36.4.2 Speed Control, to vary the flow rate over a range of atleast 1.0 to 10 m/s within 60.1 m/s or bett
43、er throughout the testsection.6.4.3 CalibrationCalibrate the mean flow rate usingtransfer standards traceable to the National Institute of Stan-dards and Technology (NIST), or by an equivalent fundamentalphysical method.6.4.4 Turbulence, with a uniform velocity profile with aminimum of swirl at all
44、speeds, and known uniform turbulencescale and intensity throughout the test section.6.4.5 Rotating Plate, to hold the sonic transducer array invarying orientations to achieve angular exposures up to 360,as needed. The minimum plate rotation requirements are 660in the horizontal and 615 in the vertic
45、al, with an angularalignment resolution of 0.5.NOTE 1Design the plate to hold the array at chosen angles withoutdisturbing the test section wind velocity profile or changing its turbulencelevel.6.5 Measuring System:6.5.1 Counter, to log the anemometer velocity componentreadings, with a count resolut
46、ion equaling or exceeding theclock rate of the sonic anemometer/thermometer.6.5.2 Recorder, with at least a 10 Hz rate and a resolutioncomparable to instrument resolution, for recording onto mag-netic or optical media the anemometer velocity componentreadings.6.6 Calipers, for transducer separation
47、distance measure-ments, with minimum tolerance of 0.1 mm.6.7 Ancillary MeasurementsAncillary pressure (60.5hPa) and relative humidity measurements (610 %) are neededfor sonic temperature and acoustic pathlength determination ifthe ambient vapor pressure is greater than 20 Pa. Thesemeasurements can b
48、e obtained from on-site instruments orestimated from nearby data sources.7. Precautions7.1 Exercise care while using gas pressurized containers.Procedures for handling pressurized gas cylinders shall beposted and observed. Perform all testing with pressurized gasesin a well-ventilated room. Use of t
49、he buddy system is recom-mended.7.2 Maintain chamber temperatures and pressures close tolaboratory temperature and pressure to minimize gradients thatcould cause convection within the chamber, but use sufficientover-pressure to prevent contamination from extraneous gases.7.3 Ascertain that acoustic reflections and apparatus vibra-tions are not contaminating results.NOTE 2Noise and vibrations generated during wind tunnel operationare potential interferents. Isolate the array from extraneous noise andvibration.7.4 En
